add onAudioPlaybackStarted callback for controls (#3309)

* add onAudioTrackReady callback for controls

* more details in controls.md for `onAudioPlaybackStarted`

src/useAudioContext.tsx

@@ -18,6 +18,7 @@ import {
 } from "./livekit/MediaDevicesContext";
 import { type PrefetchedSounds } from "./soundUtils";
 import { useUrlParams } from "./UrlParams";
+import * as controls from "./controls";
 
 /**
  * Play a sound though a given AudioContext. Will take
@@ -42,6 +43,7 @@ async function playSound(
   src.buffer = buffer;
   src.connect(gain).connect(pan).connect(ctx.destination);
   const p = new Promise<void>((r) => src.addEventListener("ended", () => r()));
+  controls.setPlaybackStarted();
   src.start();
   return p;
 }